Polymer for contact lenses

Abstract

The present invention relates to a polyurethane polymer composition prepared by reacting a mixture comprising: a} at least one polyethylene glycol, and either b) at least one poly-isocyanate, having a functionality greater than 2 or c) at least one di-isocyanate and at least one polyol or at least one macropolyol having a functionality greater than 2, wherein the polyol or macropolyol is present at an amount of 0.1 to 9 wt % of the mixture. The invention also relates to a process for preparing a polyurethane xerogel in the form of a molded article, said process comprising the steps of: i.) preparing said mixture; ii.) dispensing the reaction mixture formed in step i) into a mold; iii.) allowing the reaction mixture to react and cure; iv.) removing the molded article from the mold; and v.) hydrating the molded article.

The invention claimed is: 
     
       1. A contact lens formed from a polyurethane polymer composition prepared by reacting a mixture comprising:
 (a) 10 to 70 wt % of at least one polyethylene glycol having a number average molecular weight of 1000 or less and 10 to 70 wt % of at least one polyethylene glycol having a number average molecular weight of 3000 to 8000; 
 (b) 9 to 50 wt % of at least one di-isocyanate; and 
 (c) at least one polyol or at least one macropolyol having a functionality greater than 2, wherein the polyol or macropolyol is present at an amount of 0.1 to 5 wt % of the mixture. 
 
     
     
       2. The contact lens as claimed in  claim 1  wherein the mixture contains 5 wt % or less compounds comprising tertiary hydrogen atoms. 
     
     
       3. The contact lens as claimed in  claim 1 , wherein the at least one di-isocyanate is selected from the group consisting of methylene dicyclohexyl diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, mixtures of toluene-2,4 and 2,6-diisocyanates, ethylene diisocyanate, propylene-1,2-diisocyanate, cyclohexylene-1,2-diisocyanate, cyclohexylene-1,4-diisocyanate, m-phenylene diisocyanate, 4,4″-biphenylene diisocyanate, 3,3″-dichloro4,4″-biphenylene diisocyanate, 1,6-hexamethylene diisocyanate, 1,4-tetramethylene diisocyanate, 1,10decamethylene diisocyanate, cumene-2,4-diisocyanate, 1,5-napthalene diisocyanate, 1,4-cyclohexylene diisocyanate, 2,5-fluorenediisocyanate, polymeric 4,4′diphenylmethane diisocyanate and mixtures thereof. 
     
     
       4. The contact lens as claimed in  claim 1  wherein the polyol or macropolyol has the structure of formula I: 
       
         
           
           
               
               
           
         
         wherein at least three of X 1 , X 2 , X 3 , X 4  and X 5  are each independently an alcohol group, the remainder of X 1 , X 2 , X 3 , X 4  and X 5  are each independently H or absent, and Z is a central linking unit. 
       
     
     
       5. The contact lens as claimed in  claim 4  wherein Z represents a hydrocarbyl group, optionally comprising one or more ether, ester and tertiary amine groups. 
     
     
       6. The contact lens as claimed in  claim 4  wherein Z has a number average molecular weight of 1000 or less. 
     
     
       7. The contact lens as claimed in  claim 1  wherein the polyol is glycerol, trimethylpropane (TMP) or hexanetriol (HT). 
     
     
       8. The contact lens as claimed in  claim 1  wherein the macropolyol has the structure of formula 1a: 
       
         
           
           
               
               
           
         
         wherein each of X 1 , X 2  and X 3  is independently a hydroxyl group or an optionally substituted OH terminated alkylene chain; and 
         X 4  is H or as defined for X 1 , X 2  and X 3 . 
       
     
     
       9. A contact lens formed from a polyurethane polymer composition prepared by reacting a mixture comprising:
 (a) 10 to 70 wt % of at least one polyethylene glycol having a number average molecular weight of 1000 or less and 10 to 70 wt % of at least one polyethylene glycol having a number average molecular weight of 3000 to 8000; 
 (b) 9 to 50 wt % of at least one di-isocyanate; and 
 (c) at least one polyol or at least one macropolyol having a functionality greater than 2, wherein the polyol or macropolyol is present at an amount of 0.1 to 5 wt % of the mixture; 
 wherein the macropolyol has the structure of 1b: 
 
       
         
           
           
               
               
           
         
         wherein each p is from about 3 to about 25 and R′ and R″ represent H, more preferably, p is about 25.